Electron discharge device



NOV. 20, 1951 s 2,575,448

ELECTRICAL DISCHARGE DEVICE Filed Aug. 22, 1945 4 Sheets-Sheet l 0 =5gig i \l 4a r INVENTOR. 7 \6 PazaZ Haafi An mme%% [12$ fllfiorwey Nov.20, 1951 P. HAAS 2,575,448

ELECTRICAL DISCHARGE DEVICE Filed Aug. 22, 1945 4 Sheets-Sheet 2 Nov.20, 1951 P. HAAS ELECTRICAL DISCHARGE DEVICE 4 Sheets-Sheet 15 FiledAug. 22, 1945 INVENTOR.

Nov. 20, 1951 P. HAAS 2,575,448

ELECTRICAL DISCHARGE DEVICE Filed Aug. 22, 1945 4 Sheets-Sheet 4HVVENTDR.

By Paul l /dafi and z W4 H15 flttorney Patented Nov. ED, 1951 UNITEDSTATES PATENT OFFICE 2,575,448 ELECTRON DISCHARGE iinvlcs Paul Haas,Emporium, Pa., assignor to Sylvania Electric Products, Inc., acorporation of Massachusetts Application August 22, 1945, Serial No.612,029

13 Claims.

eectrodes in the form of discs or rings to a glass envelope portion toprovide a composite glassmetal body structure with the metallic parts,

, spaced in a predetermined manner and to which other metal parts may beattached subsequent to such sealing. I

The terms disc or ring, as used in this case, are merely descriptive tothe extent that these electrode parts need not be fiat but may be ofvarious shapes, the fundamental requirement being that each has anannular portion equal in outer and inner diameters to those of the glasstubing which forms the envelope, such annular portions conforming to theabutting ends of the tubing which, preferably, are fiat. The discs orrings are sealed into the envelope with their axes coincident with andat right angles thereto, their outer periphcries being external of theenvelope while adjacent ends of the tubin sections abut and are sealedto the conforming annular portions of the metal.

In electron discharge tubes of the character described and disclosed inmy co-pending application S. N. 563,348, filed November 14, 1944, it

is often desired to have two electrodes closely and precisely spacedalong the axis of the tube, and to have these electrodes of differentshapes. The conventional method of assembly has been to make the sealsone at a time. First, two sections of tubing are held with adjacent endsagainst the opposite sides of the fiat annular portion of an electrodewhich latter is then heated through the medium of a surrounding heatingelement until the glass melts and the seal is made. Then a secondelectrode and a third section of tubing are sealed to one of the firsttwo-sections of envelope, and so on.

Among the difiiculties encountered in this method, particularly when theelectrodes are closely spaced, is the problem of relative adjustment ofthe work and the heating means so that when the second seal is made theother electrode will not absorb enough heat to destroy the first seal.Even when the first seal withstands the reheatingit is subject toexpansion and distortion, thus limiting the precision of alignment andspacing of the electrodes particularly where high melting point glass orother vitreous material is used. It is therefore difl'icult to obtainthe same characteristics in successive tubes manufactured by thisprocess. Heretofore it has not b p sible to make both sealssimultaneously because the electrodes, being inherently of differentsizes and shapes, absorb the heat at different rates. Thus theelectrodes do not reach the sealing temperature at the same time, andthe quick-heating electrode cannot be held at the sealing temperaturewhile the other electrode comes up to temperature.

As hereinabove stated a principal object of the invention is to providean improved method of sealing these disc or ring electrode whereby twoor more electrodes, held precisely in position, are simultaneouslysealed into the envelope, thus avoiding the disadvantages resultingfromreheating the completed seals as each successive seal is made.

The invention accomplishes this object by using a method in which eachelectrode is composed of one or more pieces; the parts, one from eachelectrode, which are to be sealed to the glass are substantiallyidentical in size and shape or have substantially the same heatabsorption characteristics. Another advantage of using rings ofsubstantially the same size is that the seals have approximately thesame strain characteristics, thus assuring an hermetic or vacuumtightseal for all the rings. These similar parts of the electrodes are held,together with the glass tubing, in precise alignment and spacing and theseals made simultaneously, the parts absorbing heat at the same rate.After the seals are completed the remaining parts of the electrodes arefastened by suitable means to the parts which have alread been scaled tothe glass.

The sealed portion of each electrode need consist only of the opposingannular surfaces required for scaling to the adjacent sections of thetubular envelope and whatever additional area is required for attachmentthereto of its respective other electrode part or parts. The morecomplicated parts of the electrodes are made separately. Thisindependence of construction of the electronically active parts of theelectrode and the disc or ring members required for sealing has otheradvantages in addition to allowing more than one seal to be made at thesame time.

The manufacture of parts is simplified because it is unnecessary toprovide an annular sealing surface in the same piece with the morecomplicated electronically active parts. It is thus also possible to usemore complex electrode structures than can be used with electrodes madeas units from a single piece of metal.

The cleaning of the electrodes after sealing is simplified. Since thesealed parts of the electrodes may be small and simply shaped, they donot become so heavily oxidized during sealing.

and their surfaces are more readily accessible for the application ofcleaning fluids.

Another object of the invention is the incorporation of a simple way ofproviding electrical coupling between the electrodes or between resonantcavities which may be associated with the electrodes. The rivets orother devices used to fasten the active parts of one electrode to thesealed disc may be allowed to extend axially down the envelope intoproximity with another electrode or through an opening in anotherelectrode into the adjoining cavity.

A further object of the invention is in the fabrication of the discs orrings; to be sealed to the glass tubing, the provision of a series ofapertures therethrough whereby such parts cooperate with an assemblyfixture as means for holding themselves in true concentricity, and withstop members to limit their movement toward each other to apredetermined and exact parallel spacing as the glass tubing under endpressure becomes shorter during the sealing operation.

And, still another object of the invention is to make further use ofcertain of the apertures in the said fabricated discs to align thesealed assembly on a second fixture and to employ the others as rivet orscrew holes in the fastening of other parts to complete the electrodeassemblies.

My invention will be more fully set forth in the following descriptionreferring to the accompanying drawing, and the features of novelty whichcharacterize my invention will be pointed out in the claims annexed toand forming a part of this specification.

Figs. 1 and 2 are enlarged end view and elevation, respectively, of thetubular glass sections which form the envelope.

Fig. 3 is a greatly enlarged detail in elevation showing the long andshort rivets.

Fig. 4 is a plan view of one of two similar discs used in thatembodiment of the invention illustrated in Figs. 9, 10, 11, 11-A, 13,16, 17, 18,

21 and 24.

Figs. 5 and 6 are detail views in plan and elevation, respectively, ofthe cup-shaped anode used in both illustrated embodiments of theinventions.

Figs. 7 and 8 are views similar to Figs. 5 and 6 of the grid frame.

Fig. 9 is a longitudinal section of the disc assembly after sealing.

Fig. 10 is a view similar to Fig. 9 but showing the cup-shaped anode andthe grid frame riveted to their respective discs.

Fig. 11 is a longitudinal sectional view drawn to a still larger scaleand illustrating the disc assembly fixture and work pieces thereonbefore sealing.

Fig. ll-A (Sheet 4) is a view similar to Fig. 11 but drawn to a smallerscale and showing the parts in the relative positions they assume aftersealing.

Fig. 12 is a fragmentary view similar to Fig. 11 but with the anode andgrid discs shown as formed of thinner metal, the anode disc having aconcentric annular, reinforcing depression while the grid disc has botha depressed central portion and a downwardly turned annular flange.

Fig. 13 shows in elevation a sub-assembly of a work piece and fixturepart as will be explained. Fig. 13-A is a top plan view drawn to asmaller scale and illustrative of any suitable removable means forcentering the intermediate glass section.

Figs. 14 and 15 are top plan views of the two disc members seen in Fig.12.

Fig. 16 is a view partly in front elevation and partly in verticalsection of the heating apparatus for effecting the disc seal, the workand weights thereon being shown in full lines before sealing and indotted lines after heat has been applied.

Fig. 17 is a fragmentary view of parts seen in Fig. 16 with the heatingcoil shown in electrical diagram.

Fig. 18 is atop view of the heating coil with the work positionedtherein.

Fig. 19 is a side view of the rack and gear mechanism seen in Fig. 16.

Fig. 20 is a fragmentary detail of the coil supporting member as viewedfrom the rear wit respect to Fig. 16.

Fig. 21 is a view partly in elevation and partly in vertical section ofthe riveting fixture and the work positioned thereon the grid framebeing shown as the part to be riveted.

Figs. 22 and 23 are opposing end views of the movable punch and thefixed rivet holding member, respectively, of the riveting fixture.

And, Figs. 24 and 25 are views in elevation of the completed tubesillustrated in the two embodiments of the invention, part of Fig. 24being shown in longitudinal central section. In these views the extraanode ring is shown as added which operation is done after sealing.

In the drawing similar reference numerals refer to similar partsthroughout the several views.

Referring first to Figs. 1 to ll-A, inclusive, 13, 13-A and 16 to 24,inclusive.

At I, 2 and 3 are shown the upper, lower and intermediate sections,respectively, of glass tubing which when the electronic tube iscompleted form the envelope 4, in this instance such sections being ofdifferent lengths. Whenever the term glass is used it should beunderstood that any glass like insulating material may be used which iscapable of being softened by heat to form a seal with metal.

Spaced apart by the intermediate length of tubing 3 and in abutment withopposing ends of the sections I and 2 are two similar discs 5 and 6through each of which surrounding a central opening I are a plurality ofholes 6 of one diameter and a like number of holes 9 of a smallerdiameter, all arranged with their axes in a circle concentric with thecentral opening 1. Six of these holes are shown, three of each size,regularly spaced and alternately arranged. The discs,

} it will be observed, are of greater diameter than the gass tubing toprovide an annular exterior portion while there remains between thecentral opening and the wall of the tubing an exterior portion in whichthe concentric circle of holes is located and providing a supportingarea to which other parts, as will be explained, are attached. The discs5 and 6, in this modification, are shown as flat although for thepurposes of the invention the only flats need be the annular surfaceportions engaged by the abutting ends of the glass tubing in order thatseats be provided for the tubing and whereby the discs are spaced intrue parallel relation.

For the purpose of assembling the parts thus far described and as ameans for supporting them in assembled relation during the sealingoperation, there is mounted upon a suitable pedestal ill, see Fig. 16,shown as of ceramic material, a vertically extending post turned down toprovide a short base I I, a shoulder l2 beyond which is an elongatedupper extension l3, and a reduced lower stem l4 which is anchored in thepedestal and threaded to receive a clamping nut I5.

Slidably fitted to the post extension II are two similar opposingmembers l6 and Il comprising fiat rings from each of which extendparallel to the post a plurality of pins I8 and a plurality of tubes IS,the pins of one ring slidnbly engaging in the tubes of the other seeFigs. 11 and ll-A. These pins and tubes are also regularly spaced andarranged in a circle of like diameter as that in which the holes 6 and 6are located, the pins also having a sliding fit in the disc holes 9while the tubes are likewise fitted to the holes 6. An adapter orcentralizing sleeve 26 for the tubing 2 is slidably fitted to the basemember ll of the center post. This member, of ceramic material, restsupon the pedestal Ill and is slightly shorter than the height of theshoulder i2. A similar but longer sleeve 2i is slidably fitted v to thepost extension l3 as a means for centralizing the tubing I. This adaptersleeve is of a length to extend above the end of post extension I! butstops short of the upper end of the tubing l.

Assembly of the parts for sealing and thus providing what is hereinaftertermed the composite glass-metal envelope and body structure of thetube, while clearly illustrated in Figs. 11 and13, will be brieflydescribed as follows:

With adapter sleeve 20 positioned on the base ll of the center post andresting upon the pedestal Hi, the bottom section 2 of glass tubing isplaced thereover to also rest upon the pedestal. Ring I1 is then droppedover the post with its pins l6 and tubes l9 extending upwardly and restsupon the shoulder i2. Disc 6 is placed on the tubing 2 and centralizedtherewith by the pins and tubes i8 and i9 engaging, respectively,through the holes 9 and 8. Next the intermediate tubing section 3 isplaced on the disc 6 substantially in alignment with section 2.Preferably the disc is then slipped onto the pins l8 and tubes IQ of thering I6, as shown in Fig. 13 as a sub-assembly, after which these partsare positioned as shown in Fig. 11 with the disc 5 spaced from disc 6 bythe glass tubing 3 and with the pins iii of one ring slidably engaging ashort way into the tubes [9 of the other ring as indicated. .The adaptersleeve 2| is then placed over the post extension l3 to rest upon thering i6 and the tubing section is slipped over such sleeve into abuttingengagement with the disc 5.

As a means for precisely centering the intermediate glass section 3 anysuitable removable mechanical device may be employed such, for instance,as that illustrated in Fig. 13-A and diagrammatically in Fig. 11. Thisdevice, which may be any simple contrivance adaptable for the purpose isshown as a pair of pliers 22 having a pivotal connection at 23 while thenose pieces, when closed upon the work, have a bore 24 the wall of whichengages and. centralizes the glass tubing 3, the latter being located inrelation to the peripheral edge of one of the discs 5 or 6 by engagementtherewith of the wall of a concentric counterbore 25 in the centeringtool.

A Water-cooled high frequency, double wound induction heating coil 26 isshown, with particular reference to Figs. 16, 17 and 18, as horizontallydisposed and supported by the terminal extensions 21 and 26 thereofbeing secured by clips 29 to a plate 30 and having couplings 3i and 32with a source of water supply and a water outlot. This plate a islaterally adjustable on a bracket 56 slidable on a rod 34 extending verahand wheel 44, a set screw '45 holding the rack in any desired positionof adjustment. The electrical connections for the heating coil areillustrated diagrammatically in Fig. 13.

The rack is adjusted to raise or lower the pedestal l6 and thus move thework within the coil so as to bring the discs 5 and 6 into such positionthat the heating thereof will effect their simultaneous sealing with theglass. A weight is placed upon the upper end of the glass tubing i andcomprises, in this instance, first a ceramic disc 46 and then the weightproper 41 of suitable heavy metal.

As the glass under heat becomes softened and begins to flow the sectionsI, 2 and 3 will become relatively shorter under end pressure of theweight acting against the fixed support. Consequently as the weightdrops to the dotted line position indicated in Fig. 16 the discs 5 and 6will also settle to the dotted line positions indicated in the samefigure. In this dotted position the discs will have moved relativelycloser together, the final spacing thereof being predeterminable by thelength of the sleeve l9 which, it will be observed, act as stops byengaging the opposing inner faces of the discs 5 and 6 and at the sametime act as leveling means to hold the discs in parallel relation toeach other, as is shown in Fig. ll-A.

The seal having been made, weights 46 and 41 are removed and the workdisengaged from the fixture. At this time the assembly is as illustratedin Fig. 9 and it will be observed that the surfaces are readilyaccessible for the application of cleaning fluids.

Further assembly of the tube is as follows:

In the illustrated embodiment of the invention the anode is made ofthree parts, viz., the disc or ring 5 sealed to the glass tubingsections l and 2, a cup-shaped anode proper 48 depending through thecentral opening I and formed with an outwardly turned annular flange 49having three rivet holes 50 which register with the holes 5 and a likenumber of outwardly opening radial slots 5i which register with thelarger openings 5, and, also, an outer anode ring 52 which is solderedto the disc 5 after sealing.

The grid is made of two parts, viz., the grid disc 6 sealed to the glasstubing sections 2 and 3 and the grid frame the latter comprising anannular ring 53 preferably of like outer diameter as the anode flange 49with its center opening of like diameter as and registering with thehole I in the disc 6. This grid frame or ring carries the grid wires 54and has a like number of rivet holes 55 and outwardly opening radialslots 56 as there are similar holes 50 and slots 5| in the anode flange49, the holes 55 registering with the rivet holes 6 and slots 56registering with the holes 6 in the disc 6.

The fastening devices employed in assembling the parts of the twoelectrodes are, in this instance, shown as short rivets 51 for the oneand long rivets 58 for the other, the heads of the short and long rivetsbeing provided with reduced pilot xtensions 59 and 58, respectively,which are coaxial with the shank portions. The short rivets 51 are usedfor the grid parts while'the longer rivets 58 are used for the anode,the extensions 58 of the long rivets extending into proximity with thegrid or, as shown, through the holes 8 in the grid disc, thus providingelectrical coupling between the electrodes or between resonant cavitieswhich may be associated with the electrodes.

As shown in Fig. 21, the riveting jig or fixture is of simpleconstruction and includes the two relatively movable members of a punchpress. The press member is a post 58 upstanding from a base II andhaving an annular recess adjacent its upper end to provide a headportion 52 and a shoulder 63, the head being drilled to receive threevertically extending sleeves 64 which bottom on the shoulder 63.

' As with the assembly fixture hereinabove described, the holes 8 and 8formed in the disc members and 6 in the fabrication of these partspermit these members to cooperate with the riveting device in centeringand properly aligning the work for the riveting operation.

Preferably, the first operation is to attach the grid frame 53. To thisend a short rivet is placed on the end of each sleeve 64 where it isheld by its pilot 58 extending into the sleeve, as illustrated in Fig.21. Then with the work inverted so that the tubular section I extendsdownwardly over the post 68 the sleeves 64 registering with the holes 8in th disc 5 engage through such holes, the disc 5 resting on the rivetheads and the shanks of the rivets passing through the aligned holes 3and 55 in the disc 6 and grid frame 53.

The punch 65 is recessed to provide a head 66 and shoulder 61 similar tothe corresponding parts of the press member. This head 66 is provided,however, with six regularly spaced holes in alternate ones of which arepunch rods 68 formed to head the rivets against the grid frame 53 whilein the other holes are guide rods 69 which register with and passthrough the aligned openings 8 and slots 56 respectively, in the disc 8and grid frame 53. A spring pressed pressure pad or stripper 18 iscarried by the punch to yieldingly engage the work in advance of thepunch rods.

To rivet the flange 49 of the anode to the anode disc 5 the operation isthe same except that the long rivets 58 are used and the work isreversed so that the tubing section 2 extends downwardly over the part60. In the final operation the header II and exhaust tube 12 are sealedin the usual manner and, with the glass sections 1, 2 and 3, give thecomplete envelope 4. It may here be stated that sealed into the headerH, previously to its sealing with the tubular section 2, is the cathodesheath I3 which houses the heater-cathode assembly 14, the latterincluding the cathode grid 15, as shown in Fig. 24.

In some instances, as illustrated in Figs. 12, 14, 15 and 25, the anodeand grid discs may be made of much thinner metal, and for the purpose ofreinforcing such parts the anode disc 5 is shown as having an annulardepression 16 as the bearing surface for the tubing sections l and 3while the grid disc 6' is formed with a central depression TI, in whichthe holes I, 8 and 8 are located, and a depending annular flange 18exteriorly of the tubing, the amount of metal in the parts of the twoelectrodes exteriorly of the glass tubing being substantially the sameso as to allow substantially equal heating. Also, in this modificationan outer ring 52 is soldered to the anode disc 5".

While I have shown-and described rivets as the means for rigidlysecuring the parts of the electrodes together it will of course beunderstood that other suitable fastening devices, as screws, may beused. In this latter event the plunger member of the final assemblyfixture would be eliminated.

Furthermore, although I have shown but a single heating unit andmanually operable parts associated therewith, it will also be understoodthat, for quantity production, and without departing from the spirit ofthe invention a number of the units for the assembly and sealing of thecomposite glass-metal body structure may be mounted on theintermittently rotatable tu'rret of a machine built for such purpose.

It will also be understood that features of my invention, such as thestructural means for facilitating the alignment of the electrode partsmay be employed to produce other suitable types of electrical devices.

Although I have shown and described particular embodiments of myinvention, I do not desire to be limited to the embodiments described,and I intend in the appended claims to cover all modifications which donot depart from the spirit and scope of my invention.

What I claim is:

1. The method of fabricating a glass to metal article including thesteps of assembling a plurality of metal articles having approximatelythe same heat absorption characteristics with glass members separatingthe metal articles, simultaneously heating all of said metal articleswhereby the glass and metal attains the softening temperature of theglass, while allowing mutual approach between the metallic parts until apredetermined position obtains therebetween,

and then stopping relative movement between the metallic parts whileallowing the glass to cool and seal with the metallic parts.

2. In the assembly and glass-to-metal sealing of a composite glass-metalbody comprising a plurality of metal wafers substantially identical insize and shape and spaced apart in parallel planes by and betweensections of glass tubing coaxially aligned therewith, the method ofinsuring precise, predetermined axial spacing of said wafers, trueparallelism thereof and identical sealing-in conditions which comprisesthe steps end pressure, and mechanically arresting suchaxial movement ofsaid wafers.

3. The method of making a composite glass metal envelope and electrodebody structure for electronic tubes which comprises the steps ofarranging a plurality of metal rings coaxially with and as separatinmeans between properly proportioned lengths of glass tubing, exertingend pressure against said tubing, softening the glass adjacent saidrings by the application of heat from heating means surrounding saidrings, guid ing the relative axial movement of said rings toward eachother as said tubing sections shorten under heat and said end pressure,and stopping such movement with said rings in parallel relation and at apredetermined spacing, thereby effecting both said predetermined spacingand 9 a vacuum-tight sealing of the glass tosaid rings by a singleheating operation. I

4. The method of making a composite glassmetal envelope and electrodebody structure for electronic tubes which comprises the steps ofarranging a plurality of metal rings coaxially with and as separatingmeans between properly proportioned lengths of glass tubing, exertingend pressure against said tubing, softening the glass adjacent saidrings by the application of 10 heat from a high frequency induction coilsurrounding said rings, guiding the relative axial movement of saidrings toward each other as said tubing sections shorten under heat andsaid end pressure, and stopping such movement with said rings in trueparallel relation and at a predetermined axial spacing, therebyefi'ecting both said spacing and a vacuum-tight sealing of the glass tosaid rings by a single heating operation.

5. The method of making an electron dis- 2o charge tube which includesthe steps of vacuumtight sealing a plurality of planar parallel metalrings coaxially with and to the wall of an open ended cylindrical glassenvelope forming tube, said rings being spacers between sections oftubing forming said wall, inserting discharge electrodes into the innerperipheries of said rings, attaching said electrodes to their respectiverings, sealing a header, including a sealed-in cathodeheater assemblyunit, to one end of said wall, evacuating the tube at its other end,andsealing said evacuation end to completely form said envelope. a;

6. Apparatus of the character and for the purpose described including asupport, a rod upstanding from said support, a shoulder on said rod. anadapter sleeve on said rod below said shoulder, a second adapter sleeveslidable on said rod above said shoulder, two rings slidable on said rodand interposed between said adapter 40 sleeves, the lower ring normallyrestin upon said shoulder, alternately arranged pins and sleevesparallel to said rod and extending from the opposing faces of saidrings, said pins and sleeves being regularly spaced circumferentiallyand radially with respect to said rod and with the sleeves of oneringtelescoping the pins ofv said other ring, the free ends of saidsleeves comprising both a stop for limiting axial movement of said ringstoward each other and a support for maintaining said rings in parallelrelation when in engagement therewith.

7. The method of making electron discharge devices comprising the stepsof forming a pair of annuli with large and small holes, sealing theannulitoaxiallyalignedslasstubeswiththe small hoes on each annulusaligned with the large holes in the other annulus and with one 81855 bpositioned between theannuli, and

securing an electrode to each of said annuli with the aid of pressureapplied through the large holes in the opposite annulus.

8. The method of making an electron dischargedevicecomprisingthestepsofformingapairot annuliwithholesnearthecentralhole ofeach annulus, sealing the annuli to axially aligned glass tubeswhile holding the holes of one annulusmpredeterminedrelationtotheholcsofthe, other annulus, and with one glasstube positioned betweentheannuli,andsecuringanelectrodeto 1 each of saidannuli in predetermined relationship to said holes.-

9. The method of making an electron ischarge simultaneously sealing adevice which comprises number of conductive annuli between. sections ofu vitreous tubing in accurately controlled axial alignment and mutualspacing, and thereafter securing electrodes to said annuli.

10. The method of making an electron discharge device which includesassembling a numthe central apertures of ber of metal rings inalternating order between a number of sections of vitreous tubing,applying axialpressure to said sections of tubing, fusing the edges ofsaid tubing to make joints with said rings, and thereafter securingindividual electrode structures to said metal rings.

11. Apparatus for assembling plural metal discs to plural glass tubularsections in an alternating succession includinga post extending from abase member, a number of spacing sleeves having central aperturesslidable over said post and having outer diameters such as to fit withinsaid glass of spacing rings received on said post, interposed betweensaid sleeves and each having stop members extending through apertures insaid metal discs to engage another metal disc whereby the approach ofsaid discs to each other is limited. 13. Apparatus for assembling pluralmetal discs to plural glass tubular sections in an alternating succasionincluding a post extending from a base member, a number of spacingsleeves having central apertures slidable over said post and havingouter diameters such as to fit within said glass tubular sections wherebsaid glass sections are maintained in axial alignment and a number ofspacing rings received on said post, interposed between said sleeves andeach having tubular stop members extending through apertures in saidmetal discs to engage an adjacent metal disc whereby the approach ofsaid discs to each other is limited, each oi said spacing rings havingan extending pin passing through an aperture in one of said metal discsand received in said tubular stop member to maintain the relativeorientation of said discs.

, PAUL HAAB.

narsnnucns map The following references are of record in the file ofthis patent:

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